1. Field of the Invention
This invention relates to a boosting circuit which is designed in a switching regulator structure.
2. Description of the Related Art
In general, a boosting circuit designed in a switching regulator structure has been frequently provided to a control circuit or a fault (failure) diagnosis circuit for a safety device such as an air bag for a vehicle. The reason for this is as follows. In order to enable actuation of such a device even when a battery voltage for the device is lowered due to a fault or other matters, sufficient energy is required to be stored in an electrolytic capacitor, and in this case the stored energy W is increased as a voltage V is heightened, as represented by an equation W=1/2 CV.sup.2.
A boosting circuit (booster) used in the above application field has been conventionally designed to have such sufficient performance that it is also effectively applicable to another application field as a power source circuit, and has various advantages that the control precision for an output is excellent, an output is less fluctuated with load variation, a large amount of current can be obtained, etc.
However, the above performance of the boosting circuit which has been conventionally used does not provide a sufficient merit to an air bag control unit or the like which serves as a relatively low load. Further, in the application field to the vehicles as described above, a conventional boosting circuit has a large ON-duty for a switching operation, and thus it has large rush current in a switch-on operation. Therefore, the conventional boosting circuit frequently has large noises because of its large On/Off current, and thus a countermeasure for preventing affection of the noises on an Electro-Magnetic Compatibility (EMC) must be separately provided. The circuit construction for obtaining the above performance which is not required for the air bag control unit or the like is more complicated, and thus the cost of the boosting circuit having such a complicated circuit construction is high.